Coke is a solid carbonaceous fuel that is derived from coal. Because of its relatively few impurities, coke is a favored energy source in a variety of useful applications. For example, coke is often used to smelt iron ores during the steelmaking process. As a further example, coke may also be used to heat commercial buildings or power industrial boilers.
In a typical coke making process, an amount of coal is baked in a coke oven at temperatures that typically exceed 2000 degrees Fahrenheit. The baking process transforms the relatively impure coal into coke, which contains relatively few impurities. At the end of the baking process, the coke typically emerges from the coke oven as a substantially intact piece. The coke typically is removed from the coke oven, loaded into one or more train cars (e.g., a hot car, a quench car, or a combined hot car/quench car), and transported to a quench tower in order to cool or “quench” the coke before it is made available for distribution for use as a fuel source.
The hot exhaust (i.e. flue gas) is extracted from the coke ovens through a network of ducts, intersections, and transitions. The intersections in the flue gas flow path of a coke plant can lead to significant pressure drop losses, poor flow zones (e.g. dead, stagnant, recirculation, separation, etc.), and poor mixing of air and volatile matter. The high pressure drop losses lead to higher required draft which can lead to leaks and a more difficult to control system. In addition, poor mixing and resulting localized hot spots can lead to earlier structural degradation due to accelerated localized erosion and thermal wear. Erosion includes deterioration due to high velocity flow eating away at material. Hot spots can lead to thermal degradation of material, which can eventually cause thermal/structural failure. This localized erosion and/or hot spots can, in turn, lead to failures at duct intersections. For example, the intersection of a coke plant's vent stack and crossover duct is susceptible to poor mixing/flow distribution that can lead to hot spots resulting in tunnel failures.
Traditional duct intersection designs also result in significant pressure drop losses which may limit the number of coke ovens connected together in a single battery. There are limitations on how much draft a coke plant draft fan can pull. Pressure drops in duct intersections take away from the amount of draft available to exhaust flue gases from the coke oven battery.
These and other related problems with traditional duct intersection design result in additional capital expenses. Therefore, a need exists to provide improved duct intersection/transitions that can improve mixing, flow distribution, minimize poor flow zones (e.g. dead, stagnant, recirculation, separation, etc.), and reduce pressure drop losses at the intersection thereby leading to improved coke plant operation as well as potentially lower costs to design, build, and operate a coke plant.